This invention relates to the formation of tubular webs of material, in particular of heat-sealable material.
It is known to package products by placing discrete quantities of the product at intervals along the length of a generally flat web of material, folding over and sealing together the side margins of the web and then dividing and sealing the web transversely between the successive quantities of the product to enclose them in separate packets. It is also known to use a web of a heat-sealable material so that the seals are made by welding. Thus the flat web carrying doses of the product has its side margins folded over and the edges pinched together and heated by a pair of rollers on substantially vertical axes to produce a raised seam weld.
In most instances it is necessary to press the raised seam weld flat, especially if a number of the packets are to be packaged together in an orderly arrangement as is often the case with infusion packets such as tea bags, so an additional operation is needed to complete the formation of the tube. A further and sometimes more significant feature of the known method is that the width of material employed in the seam weld does not add to the capacity of the packet.
It is an object of the present invention to avoid both these disadvantages.